The present invention concerns antibiotic-natural polysaccharide polymer adducts based on non-covalent and non-ionic bonds, with an improved profile of activity compared with the corresponding antibiotic.
Many difficulties arising out of the chemotherapeutic treatment derive from the fact that some active principles do not possess optimum pharmacological and pharmaco-kinetic characteristics. One of the approaches used by the pharmaceutical technique to face the problems caused by a low bio-availability or a limited duration of the antibiotic effect, following oral or parenteral administration, consists in bonding the antibiotic to natural or synthetic, inert and bio-compatible polymers. However, the tests conducted in the bonding sector with polymers have reached a limited and, in particular, scarcely foreseeable, success. Grishin G. I., Tr. Leningrad, Khim-Farm. Inst. (1969), 27, 113-18, describes the interaction between penicillins or tetracyclines and some natural polysaccharides of microbic origin. The result of these interactions is far from being quantifiable and qualifiable, since, in some cases, the interaction is absent or low, in other cases it actually exists but does not produce any effects on in the antibiotic activity. This may be ascribable to a variety of reasons, such as the nature of the bond and the relationship between the molecules.
The antibiotic-polymer associations that have proved to be successful concern classes of well-defined antibiotics or single antibiotics, and are often characterized by the formation of covalent or ionic-bond complexes or conjugates, The patent application EP 0 392 487 (in the name of Takeda Chemical Industries Ltd.) describes a complex consisting of an anthracyclinic antibiotic bearing an aminosaccharide residue and a polyanion described as a natural or synthetic polymer with negatively charged residues, capable of forming ionic bonds with the positively charged aminosaccharide residues. Compare with the antibiotic, this complex has better characteristics of stability with at neutral pH, and this allows the production of slow-dropout release preparations, free of irritating effects on tissues.
The EP 0 428 486 patent (in the mane of Sandoz Ltd.) claims a water-soluble polimixin conjugate with a carrier, e.g. a polysaccharide such as dextran, which has a higher half-life and power activity compared to native poliximin. This conjugate""s bond is of the aminic or carbamate type, i.e. covalent.
Molteni L., Optimization of Drug Delivery, Alfred Benzon Symposium 17, publishers: Hera Bundgaard. Anne Bagger Hansen, Helmer Hafod, Munksgaard, Copenhagen, 1982, deals discusses with the interaction of various types of substances, among which some antibiotics and polysaccharides, e.g. dextrans or inulin. The interaction is clearly of the covalent type because, due to the low chemical reactivity of polysaccharides and the presence of a number of hydroxilylic groups, the interaction Is said to be based on ester bonds with substances possessing carboxylic groups, or the hydroxylic groups may be oxidized to aldehydes or be replaced with reactive groups.
The covalent/ionic bonded polymer-antibiotic conjugate does not provide sure dependable results and, moreover, it represents and expensive and complex approach, from the a regulatory standpoint, to the solution of the activity problems, mentioned above, because (being chemical entities based on strong bonds, such as the covalent and ionic bond) these conjugates, which are pro-drugs, are considered as new compounds and it is necessary to characterize them chemically, to study their pharmaco-dynamic profile and clinical effectiveness.
The patent application EP 0 438 747 (in the name of Shionogi Seiyaku Kabushiki Kausha) claims a stable freeze-dried product composed of a glycopeptidic antibiotic and a water-soluble saccharyde, such as a polysaccharide (e.g. dextran), which is used in low percentages and has the function of a support stabilizer during the freeze-drying process. The glycopeptidic antibiotics, such as vancomycin are very particular drugs, particularly complex from a chemical standpoint, not orally administerable and, in a few cases, such as vancomycin, not even intramuscularly. In some cases, they may be highly nephrotoxic.
A composition containing a pharmaceutical or diagnostic agent and dextran is disclosed by the U.S. Pat. No. 4,315,002. Said agent may be an antibiotic or an enxyme and the composition is particularly suitable for sensitive pharmaceutical active compounds and enzymes for diagnostic purposes and for biochemical analyses.
It has been now surprisingly found that antibiotic-natural polysaccharide adducts, characterized by weak bondsxe2x80x94such as, for example, the hydrogen bondxe2x80x94compared to the same free antibiotic, have an equal or higher microbiological activity or therapeutic effectiveness, with reduced molar doses of the antibiotic and, inter alia, are less toxic.
The object of the present invention is represented by antibiotic-natural polysaccharide adducts, in which the interaction between the two components is based on non-covalent and non-ionic bonds.
More specifically, the adducts of the present invention contain an antibiotic selected from the group consisting of xcex2-lactam, aminoglycoside and macrolide antibiotics, linked by a non-covalent and non-ionic bond to a natural polysaccharide.
Among the preferred antibiotics preferred according to the present invention penicillins such as amoxicillin; cephalosporins such as cefadrin, axetilcefuroxime, cefazolin, cefotaxime and cefotriaxone; aminoglycosides such as neomycin, gentamicin, amikacin and apramicin; macrolides such as erythromycin, roxitromycin and azytromycin are cited. Amoxicillin, cefadrin and gentamicin are particularly preferred.
The polysaccharides useful for the present Invention are biocompatible and inert and, therefore, have no effects from a pharmacological and toxicological standpoint. They are possibly preferably selected among dextrans, inulin and maltodextrin. For the purposes of the present invention, a special preference is given to dextrans.
Dextrans are hydrophilic and water-soluble polymers, stable to against the enzymatic attack, consisting of linear chains of (-D glucose molecules. Their molecular weight ranges from 1,000 Dalton (dextran 1) to 110,000 Dalton (dextran 110). Dextrans having a molecular weight below 4,000 Dalton, are completely excreted eliminated in the urine within 48 hours, while those having higher molecular weights remain in circulation for longer periods. For the uses of the present invention, the preference is given to dextrans 4-70, i.e. having a molecular weight ranging from 4,000 to 70,000 Dalton.
According to the present invention, the antibiotic percentage over the total adduct may range from 20% to 60% by weight.
The bond between the antibiotic and the polysaccharide in the adduct of the present invention is of the non-covalent and non-ionic type, as may be easily deduced from the mode of preparation of these adducts, requiring a co-solution in water of the polysaccharide and the antibiotic and the remotion of the solvent by known thecniques such as lyophilization and spray drying. This allows the hydrophilic interaction between the OH groups, either carboxylic or not, of the antibiotic and those of the polysaccharide, through weak bonds so called just because they need for less energy (approx. 3-5 kcal/mol.) to be crackedbroken, compared to covalent and ionic bonds, which require an energy of at least 50-100 kcal/mol. As shown In Remington""s Pharmaceutical Science, XVIII ed., page 186 seq., where these adducts are named xe2x80x9cmolecular complexesxe2x80x9d, the kind of interaction may be of various type (from the hydrogen bond to the hydrophobic interaction to the charge transfer).
The adducts of the present invention are obtained through quick and economical processes, compared to the traditional approaches that use a covalent bond between the antibiotic and the polysaccharide carrier and therefore they constitute products having now characteristics.
Therefore, another objective of the present invention consists in the process necessary for preparing antibiotic-natural polysaccharide adducts comprising the dissolution of the two adduct components in distilled water, so as to obtain a limpid solution, the tittering and the isolation of the adduct from the solvent through adequate techniques.
The process of the present invention may optionally require the presence, during the dissolution phase, of solubilising and buffer agents and preservatives.
In the case of injectable preparations, the distilled water used in the process of the present invention is depyrogenated and sterile water for injectable use; moreover, the solution is sterilized through 0.1 to 0.45 xcexcm (preferably 0.2 xcexcm) filters and divided among depyrogenated and sterilized vials, operating under a laminar flow hood, in a sterile ambient.
Preferably, the technological processes used for the isolation of the adduct from the solution are freeze drying and nebulization (spray drying), that to allow the yielding of a product in an physical form optimal for the subsequent formulation.
The adduct obtained through a the nebulization process is a light, white, water-soluble powder, especially fit for the preparation of oral formulations administrations (tablets, capsules, granules). The freeze-dried product, particularly suitable for injectable preparations, has a compact and whitish appearance and, if previously depyrogenated and sterilized, immediately restore the limpid solution of the physiologic-pH adduct through the addition of water for injectable applications.
Considering the observations made above, a further aspect of the present invention concerns the compositions prepared by freeze drying or spray drying of natural antibiotic-polysaccharide adducts described above.
The formation of these adducts favourably modifies some of the pharmacological pharmaco-kinetic characteristics of the antibiotic. In fact the adducts with low molecular weight polysaccharides can increase the solubility of a low soluble antibiotic and, then, its bio-availability when administered by oral route. In case of injection therapy, the us of a high molecular weight polysaccharide allows the extension of the circulation time and, consequently, prolongs its effect.
The adduct activity has been measured in vitro using the methods explained below, in examples 5 and 6, and in vivo, by administering rats infected by a strain sensitive to the antibiotic in question (examples 7 and 8).
The present invention also comprises includes the use of antibiotic-natural polysaccharide adducts based on non-covalent and non-ionic bonds, for the treatment of pathologies in humans and animals.